This invention relates to molding compositions. In one of its more specific aspects this invention relates to thermoplastic molding compositions. More particularly, the invention relates to thermoplastic molding compositions containing polar compounds. In another aspect of the invention it relates to a method for molding thermoplastic molding compositions. More particularly, the invention specifically relates to the use of energy of microwave frequency in molding thermoplastic compositions. In yet another aspect the invention relates to objects molded of thermoplastic molding compositions.
In the past, microwave energy has been used in vulcanizing techniques to raise the temperature of vulcanizable compositions containing polar compounds to a level at which vulcanization can be accelerated by conventional means. It has now been discovered that microwave energy can be used to increase the temperature of polymer/resin compositions containing polar compounds above the softening point to permit low pressure molding. A number of polar components and polymers that will work well to promote the start of vulcanization using microwave energy are not, however, useful in promoting softening of thermoplastic compositions. Temperatures obtained within practical time cycles are not enough to overcome the flow deficiency caused by the addition of solid nonthermoplastic polar polymers such as halogenated rubbers, nitrile rubbers, and/or fillers such as carbon black. It should also be pointed out that highly filled resins do not react well to microwave energy so that highly filled thermoplastic elastomer based stocks result in lower melt flow rates because of lesser percentages of polymer in the total composition. Limited compatibility with thermoplastic elastomers also contributes to lack of efficiency of some ingredients which proved useful in promoting vulcanization, but are not useful in promoting softening of thermoplastic compositions. Overall, it has been found that polar compounds useful in thermoplastic compositions used in low pressure molding must be selectively chosen.
It is therefore an object of this invention to provide compositions of matter that can be molded at pressures below about 200 psig. More particularly, it is an object of this invention to provide thermoplastic molding compositions containing polar compounds that can be molded at low pressures. It is another object of this invention to provide a method for molding thermoplastic compositions containing polar compounds. More particularly, it is an object of this invention to provide a method for molding thermoplastic compositions using energy at microwave frequencies in the molding process. It is still another object of this invention to provide molded objects of thermoplastic molding compositions containing polar compounds.
Other aspects, objects, and the various advantages of this invention will become apparent upon reading this specification and the appended claims.